Second-order perturbation theory with a density matrix renormalization group self-consistent field reference...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Accurate electronic structure calculations are crucial for understanding molecular properties.
• Conventional methods struggle with systems exhibiting strong electron correlation.
• Multireference systems, like transition metal dimers, pose significant computational challenges.

Purpose of the Study:

• To introduce a novel computational method, DMRG-CASPT2, for treating complex electronic correlation.
• To address limitations of existing methods in describing non-dynamical and dynamical correlation simultaneously.
• To provide a robust tool for studying demanding multireference systems.

Main Methods:

• Development of a second-order perturbation theory based on a Density Matrix Renormalization Group Self-Consistent Field (DMRG-SCF) reference.
• Implementation of the DMRG-CASPT2 method, which converges to CASPT2 with a sufficiently large DMRG reference.
• Application to the potential energy curve of the chromium dimer using a large active space (28 orbitals).

Main Results:

• The DMRG-CASPT2 method accurately describes both non-dynamical and dynamical correlation effects.
• Calculations on the chromium dimer with a large active space resolved issues of overestimation in dissociation energy and sensitivity to the zeroth-order Hamiltonian seen in smaller active spaces.
• Demonstrated the method's capability on a challenging multireference system.

Conclusions:

• The DMRG-CASPT2 method offers a significant advancement in electronic structure calculations for complex molecules.
• This approach overcomes limitations of traditional CASPT2 by effectively handling large active spaces and strong correlation.
• The study validates the method's accuracy and applicability to demanding systems, paving the way for future research in correlated electron systems.